Method of screening pulp.



A. J. HAUG.

METHOD OF SCREENKNG PULP, APELICATION FILED MAR. 3, I917.

j fi 1 5 Patented N0v..13, 1917 UNITED STATES ATENT OFFICE.

ANTON J. HAUG, OF NASHUA, NEW HAMPSHIRE, ASSIGNOR 'lO IMPROVED PAPER MACHINERY COMPANY, OF NASHUA. NEVJ HAMPSHIRE, A CORPORATIQN OF MAINE.

METHOD OF SCREENING PULP.

Specification of Letters Patent.

Patented Nov. 13, 191 '7.

To all whom "it may concern:

Be it known that l, Ax'ron J. HAUG, a citizen of the United States, and a resident of Nashua, county of llillsborough, State of New llampshire, (whose post-ollice address is care of linproved laper i\lachinery Company, Nashua, New llampshire,) have invented an improvement in Methods of Screening Pulp, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts:

This invention relates to methods of screening paper pulp, the object being to secure a more effective screening action in the case of certain kinds of pulp which are ditlicult efiectively to screen by the ordinary screening methods.

Although the invention is not limited in its application to any particular class of pulp or any particular method of screening, it is especially adapted to overcome ditlieulties encountered in the centrifugal screening of such pulp as chemically prepared pulp, where I have found that the coarser rejections tend to form clusters with the finer fibers and clog the screen and impede the screening action.

In the case of a mechanically reduced pulp, such as one disintegrated by grinding, the coarser ragments consist chiefly of impurities together with large slivers and pieces of wood which the grinding agencies have failed completely to reduce. As contrasted with the coarser fragments in a chemically prepared pulp, these coarser particles in a mechanically prepared pulp are relatively stitf or unyielding and non-absorbent and non-clinging. They permit a ready drainage of the shower water which,

allows the finer fibers to be washed and freed therefrom and they have little tendency to cling to the liner fibers.

Chemically prepared pulp is characterized by long fibers mingled with a certain proportion of coarser material consisting of knots and slivers which have not been entirely opened up by the chemical process These fibers have a tendency to interlock and form clusters when slightly disturbed an agitated, which is the condition under which the pulp enters the screen. If coarser,

uncooked particles are in the clusters and the liquid is suddenly withdrawn, as happens in the case of the ordinarv centrifugal screen when the pulp is applied to the screening surface, it is ditlicult to separate the finer fibers from the uncooked slivers because the long, fine fibers are llexible and tend to cling te'mieiously to the slivers when the water is drained therefrom. The application of shower water is of little eil'ect in washing oil' the finer fibers, since a certain quantity of water is absorbed by the clusters, rendering them practically innnune after the washing action of the water and they simply roll themselves away from the wzrt er as the water drains away. The result is that the water passes through the screen while the unseparated clusters of fibers cling to the screen and clog it.

By suspending the clusters of a chemical pulp in liquid, however, they can be readily opened up and, while in this state of liquid suspension, the uncooked particles or rejections can be easily separated from the finer fibers by means of agitation.

This characteristic 1 avail myself of in my improved method by applying the pulp to a screening surface and there maintaining it in a fluid mass, wherein the unscreened fibers are kept in a state of liquid suspension, so that by agitating the mass, the fibers are permitted to separate and pass through the screen, the tailings or rejections being withdrawn through a tailing outlet.

. The invention will be best understood by reference to the following description when taken in connection with the accompany ing illustration of one specific device for carrying it into effect, while its scope will be more particularly pointed out in the appended claims.

' Referring to the drawings, I have therein shown my invention as applied to a form of centrifugal screen. The latter comprises the casing member 1 containing the sta tionary screen drum 2, the latter of any usual or ordinary construction. The pulp is fed to the interior of the screen through the pulp inlet 3 and the annular feed orifice 4: through which it is dischargedunder an appropriate head or pressure. \Vithin the screen there is mounted an agitating device consisting of a plurality of agitating blades 5 mounted upon the central shaft 6 which may be rotated by the pulley 7, so that the blades are rotated in close=proximity to the interior surface of the screen drum 2, serving to'kcep the pulp Within the same in a state of constant agitation. In the case of the ordinary centrifugal screen, the flow of the pulp across the screening surface and toward the tailings outlet, herein indicated at 8, is unimpeded and is often accelerated by feeding devices, such, for example, as inclined impeller or agitating blades, the inclination of which is such as to feed or force the pulp across the screen from the inlet end to the tailings outlet.

In the present case I oppose the general impulse or tendency which the head of the pulp and the centrifugal action of the rotary blades give the pulp to tlow freely across the screen to the tailings outlet, by so inclining those blades with reference to the direction of rotation that they tend to force the stock back away from the tailings outlet and toward the inlet end of the screen. This opposes the natural How of the pulp, whether such flow is due to a head ,or other causes, and tends to backthe stock up in mass on the screen and maintain the pulp against the screen in a fluid mass, wherein the unseparated fibers are kept in a state of liquid suspension. By this means there is maintained at all times a fluid mass of stock on the inside of the screen which .tends to hold in suspension or immersion the stock fibers so that they tend to separate from the tailings and pass through the screen instead of forming clusters and being spread over the screen as the water drains away, as in the old practice. This liquid mass is kept constantly agitated by the rotary blades so as to permit the fibers to separate and pass through the screen while the coarser particles gradually work out toward the tailings outlet in virtue of the centrifugal action of the blades in conjunction with the resistance of the finely perforated screen plate, the head or pressure of the mass, and the rapid accession of additional quantities of stock through the inlet 4. These forces somewhat more than counteract the opposite or backward impulse given the stock by the inclination of the agitating blades so that the coarser rejections or tailings pass off the end of the screen and into the tailings out-,

let 8, the finer fibers passing into the screen stock outlet 9 in the direction shown by the arrows.

This method of handling the stock keeps the unscreened pulp in an agitatetih fluid mass against the screening surface sothat under this agitation the clusters, being in a state of liquid suspension are readily opened up, the finer fibers readily separated therefrom and carried through the screen, and the coarser rejections or tailings gradually worked along toward the tailings outlet.

In the illustrated form of screen, there is provided means for introducing water to add to the liquid mass of the pulp being agitated on the screen. Herein the water is admitted to an annular water chamber 10 through the feed pipe 11 and discharged radially outward through an annular water discharge orifice 1:2, this being preferably located so that it dilutes the pulp and increases the liquid volume thereof near the outlet end of the screen. This helps increase the liquid vohune of the screened pulp and also helps to maintain a head near the outlet so that the rejections may be kept well in suspension while being agitated up to the time of their discharge from the screen. The introduction of this thinning water is not essential, but may be desirable for certain kinds of pulp, as, for example, where there is a. large percentage of rejections. By following out this method of screening the pulp, the tailings instead of being spread upon the inside of the screen and washed with shower water, are carried ofi under the head of the pulp while kept in suspension and agitated.

lVhile I have herein shown and described for purposes of illustration one preferred method of carrying the invention into effect, it is to he understood that the same is not limited to the mechanical details shown nor to the specific steps described in carrying it out, but that wide variations may be made in the described process without departing from the spirit of the invention.

Claims:

1. The method of screening pulp which consists in applying the pulp under centrifugal action and under a head to a screening surface. opposing the flow of the pulp to the tailings outlet by imparting to it a general impulse in the opposite direction, thereby maintaining the pulp in a fluid mass against the screening surface and keeping the fibers in a state of liquid suspension, agitating the mass to permit the hbers to separate and pass through the screen, adding water to increase the bulk of the mass and hold the tailings in suspension while being agitated and withdrawing the tailings by the movement of the mass under centrifugal action and the head of the pulp toward the tailings outlet,

2. The method of screening pulp which consists in applying the pulp to a. screening surface, opposing the flow of the pulp toward the tailings outlet to maintain the same in a fluid mass against the screenin surface, and keeping the fibers in a state 0 liquid suspension, agitating the mass to permit the fibers to separate and pass throu h the screen, and withdrawing the tailings by the movement of the mass toward the tailings outlet.

3. The method of screening pulp which consists in maintaining the pulp by centrifugal action in a fluid mass a ainst the screening surface to keep the here in a state of liquid suspension, agitating the mass weenie to permit the fibers to separate and pass through the screen, and withdrawing the tailings by movement of the mass toward the tailings outlet.

The method of screening pulp which consists in maintaining the pulp by centrifugal action in a fluid mass against the screening surface, agitating the same thereon, and. withdrawing the tailings,

5. The method of screening pulp which consists in applying the pulp under centrifugal action to a screening surface, opposing the flow or. the p lg) to the tailings outlet by imparting to it a general impulse in the oppoeite direction thereby maintaining the pulp in a fiuitl mass against the screening sin-taco and keeping the lib-21's in a state of liquid suspension, itating the mass to perinit the fibers to separate and pass through the screen, and withdrawing the tailings by the ino cnient of the mass toward the tailings outlet.

(3. he method 01 screening pulp which consists in applying pulp under centrifugal action to a screening surface, opposing the flow of the pulp toward the tailings outlet to maintain the same in a fluid mass against the screening surface and keeping the fibers in a state of liquid suspension, agitating the mass to permit the fibers to separate and pass through the screen, and withdrawing the taiiings by the movement of the mass toward the taiiings outlet.

7. The method of screening pulp which consists in causing the pulp to flow upon a screening surface, and opposing by agitation the natural flow of the pulp over the screening surface.

8. The method of screening pulp which consists in applying the pulp under centrifugal action to ascreening surface, agitating the same, and imparting to it by said agitation a. movement contra 'y to the natural flow of the pulp upon said surface.

In testimony where-oil have signed my name 1J0 this specification.

ANTQN J. HAUG. 

